Slot apparatus for high velocity gas treatment of moving webs



E. C. BROWN Aug. 27, 1968 SLOT APPARATUS FOR HIGH VELOCITY GAS TREATMENT OF MOVING WEBS Filed Dec. 22, 1966 United States Patent 3,398,466 SLOT APPARATUS FOR HIGH VELOCITY GAS TREATMENT OF MOVING WEBS Ernest Charles Brown, Danvers, Mass., assignor to Wolverine Corporation, Cambridge, Mass., a corporation of Massachusetts Filed Dec. 22, 1966, Ser. No. 603,991 1 Claim. (Cl. 34-160) ABSTRACT OF THE DISCLOSURE A multiple cross slot apparatus for high velocity gaseous surface treatment of moving wide webs has for each cross slot an individual separate cross plenum tube of small cross-sectional area co-extensive in length with each cross slot. The cross tubes are fed from a common upstream master plenum chamber of large cross-sectional area through rows of laterally spaced feed tubes connecting the master plenum chamber with each cross tube so that gases emitted from the slots may be exhausted not only laterally through spaces between the cross tubes but also both laterally and longitudinally through spaces between the feed tubes.

This invention relates to chambers or dryers in which high velocity air or other gas is emitted through a series of slots extending in parallel succession transversely across a web of material being treated while moving past the slots, either below the slots, above the slots or between opposing sets of slots.

As slots in such dryers are lengthened to accommodate greater and greater widths of material, uniformity of treatment across the width of the web becomes more and more diflicult. To insure uniform gas flow along the whole length of a slot, it is a practical necessity to provide a pressure chamber of relatively large cross section extending across the dryer and communicating with the slot so that there will be no pressure drop along the length of the slot. However, the interposition of such large plenum chambers, often in the form of a single plenum common to the whole succession of slots as in Australian Patent No. 122,672, restricts the cross-sectional areas, in a multiple-slot dryer, of the spaces forming pathways for exhausting the air after its impingement on the work. Such restriction causes variation in the velocity of the air moving laterally out between the slots, thus subjecting the edges of the web to more weight of air in a given time than the middle sections with resulting variation in treatment across the width of the web.

This cross-sectional area becomes critically small as the slots are moved closer together, unless the plenum is enlarged vertically to increase the height of the intervening spaces. But this complicates the construction and makes maintenance of the slot alignment difficult to an ultimate point of impracticability if high velocity movement of the gas is contemplated. If on the other hand, the crosssectional area of the plenum chamber is reduced by providing separate cross-plenum chambers for each slot so that there will be space between each chamber, then a pressure drop along the length of each chamber occurs and upsets the uniformity of gas flow from the slots crosswise of the web.

Heretofore the difiiculties of arranging adequate interslot cross-sectional area for exhausting the emitted gases consistent with the provision of adequate plenum crosssectional area to insure uniformity of gas flow through the slots has caused discard of slot construction and substitution of spaced tubular nozzles, as illustrated, for example, in Dapses Patent No. 3,060,595, which permit vertical rather than lateral exhaust of the emitted gases thus reducing the distance that gas emitted from any one nozzle travels laterally before being removed from the treating zone. Multi-nozzle construction is, however, more complicated and more expensive than multi-slot dryer construction.

The present invention solves the problem of providing uniform slot flow at high velocity independently of the length of the slot, while simultaneously providing large cross-sectional areas for lateral exhaust of gases emitted from the slots, thereby making it possible to use the less expensive slot construction while attaining a treatment of very wide web widths which is very nearly as uniform as that provided by vertical exhaust nozzle dryers.

This is accomplished by utilizing a separate plenum for each slot of much smaller cross-sectional area than can supply air uniformly across the entire length of the slot by end feed to the plenum, so that space may be left between the cross plenums and then overcoming the problem of pressure drop over the length of the small plenums by feeding air to each small plenum through multiple spaced feeds leading from a main plenum which is located remote from the slots. The feeds are in the form of tubes spaced apart not only longitudinally of the web but also laterally, thus permitting withdrawal of air emitted from the slots both longitudinally and laterally of the web motion from the spaces between the feed tubes. The area factor in the equation CFM=Area Velocity is thus increased, permitting movement of a greater weight of air without so much velocity variation thereby more nearly equalizing the rate of flow of exhausting air across the width of the web.

A typical gas distribution system in accordance with this invention is shown in the accompanying drawings, wherein:

FIGURE 1 is an isometric view, broken away in both directions to indicate extent, and for clarity, of an assembly for controlling the uniform flow of gas in a multiple-slot dryer;

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 1; and

FIG. 4 is an isometric view taken cross-sectionally along the line 4-4 of FIG. 3.

In FIG. 1 there is shown a casing 10 provided at its far end with an exit slot 11 through which emerges a web of material W being fed through the dryer, either selfsupported, on tenters or on a supporting belt, open-mesh or otherwise.

Supported within the casing 10 and spaced from the walls thereof by any suitable means as known in the art, is an assembly which includes a main rectangular upper plenum chamber 12 formed by a top wall 14, bottom wall 16 and opposed side and end walls one of which side walls is shown at 20. Cylindrical feed tubes 18 are attached to the bottom wall 16 with their bores communicating with the plenum chamber 12.

The bottoms of the feed tubes 18 are connected together by cross tubes 30 which have top walls 31, upper parallel side walls 32 and 33, lower tapering side walls 34 and 35 which terminate in parallel walls 37, 38 leading to a slot 39. Preferably each tube also contains a perforated crossplate 40 for further equalizing the distribution of air to the slots 39.

The perpendicular tubes 18 and their underlying attached cross-tube and slot structure are repeated at intervals down the length of the casing.

The cross-sectional area of the cross tubes 30 is not sufiicient to insure even distribution of air if it were all introduced at the ends of the tube. By providing the multiple feeds 1 8 for each tube 30, the air flow through each slot 39 can be uniform throughout its length and is independent of the length of the slot as more feed tubes are added as the length of the slot increases.

The arrows in FIG. 1 indicate how the gases may exhaust laterally and be drawn up around the side wall 20 on each side and around the end walls of the upper main plenum chamber and then exhausted from the casing by any convenient means such as blower 42. Spaces are also left at both the outgoing and ingoing ends of the dryer for removing air longitudinally beyond the ends of the main plenum 12.

'As can be seen from FIG. 3, the area indicated generally by A, B, C, D has much greater vertical height and cross-sectional area than it would if the cross tubes were connected longitudinally to form a common plenum chamber at the level of the cross tubes. In addition, there is the cross-sectional exhaust area K, L, M, N provided in the spaces between the feed tubes 18 in each row above the cross-tubes 30, as shown in FIG. 2. One thus does not sacrifice uniformity of slot flow across the apparatus by reason of the use of the small cross-sectional area cross tubes 30 because of the provision of the multiple-feed tubes 18 which, without wholly obstructing the space above the cross tubes 30, provide the multiple feed that is necessary to avoid pressure drop along tubes 30.

It can be understood that by enlarging casing 10, a similar assembly may be provided below the web W for simultaneously treating the other side of the moving web W, or the distribution assembly can be inverted and used solely below the moving web.

Since the provision of means for creating difierential pressure between the main plenum chamber 12 and the zone of web treatment is wholly conventional, it is shown only diagrammatically as a fan or fans 42 exhausting the casing, while one of several air inlets to the main plenum chamber 12 is also diagrammatically illustrated at 50 for supplying air of preconditioned temperature to the chamber 12.

What is claimed: 1 r. 1. In apparatus for treating a wide moving web by impingement of high velocity gas emitted from a series of parallel slots onto at least one surface of the web as it moves past said slots, an assembly for improving the width-wise uniformity of treatment of the web compriswalls defining a main plenum chamber,

parallel lateral rows of spaced separate feed tube's extending perpendicularly from one wall of said chamber with their bores communicating at one end with said chamber,

a series of spaced cross tubes extending parallel to said one chamber wall, each cross tube connecting, and communicating with the other ends of the bores of the feed tubes in one of said rows,

a slot in each cross tube opposite said feed tubes, and

means for continuously maintaining 'a difierential between the gas pressure in said main plenum chamber and the gas pressure beyond the outer sides of said assembly for continuously removing gases emitted from said slots not only from spaces between said cross tubes but also from spaces both between the feed tube in dilferent rows and between the feed tubes in each row.

References Cited UNITED STATES PATENTS FREDERICK L. MATTESON, JR., Primary Examiner.

H. B. RAMEY, Assistant Examiner. 

